244 



Kraus and Hunt — Sulphur and Celestite. 



C. Chemical Composition of the Celestite. 



A number of clear, transparent crystals were selected for 

 an analysis and the following results obtained : 



I. II. Average. 



Si0 2 ... 0'22 0-23 0-225 



^q 3 | 0-15 0-13 0-140 



Cab! 0-45 0-47 0-460 



MgO __ 0-12 0-14 0-130 



BaO 1-26 1-32 1-290 



SrO 53-75 53-78 53*765 



S0 o 43-58 43-60 43-590 



99-53 



99-67 



99-600 



The measured crystals possess a specific gravity of 3'979. 

 The determinations were made by means of the hydrostatic 

 balance at a room temperature of 19*5 C, while that of the 

 water was 20*5° C. 



D. Natural Etch Figures on Celestite. 



While examining the crystals from the Woolmith quarry, it 

 was observed that many of the faces showed natural etch 

 figures. Closer examination, however, showed that these 



figures could not be studied as 

 well as those noted on some crys- 

 tals obtained from the Island of 

 Put-In-Bay, Lake Erie, where ce- 

 lestite also occurs in large quan- 

 tities. 



The natural etch figures are 

 well defined and their form as 

 well as their position on the vari- 

 ous faces show conclusively the 

 symmetry of the holohedral class 

 of the orthorhombic system. 

 Figure 3 shows these figures upon 

 a crystal from Put-In-Bay. In 

 form and distribution they are 

 very similar to the artificial etch figures observed by Prendel.* 

 The solvents used by Prendel were sulphuric acid in one case 

 and potassium carbonate and hydrochloric acid in the other. 

 To our knowledge, natural etch figures on celestite have never 

 been described. 



We are indebted to Prof. E. D. Campbell, Director of the 

 Chemical Laboratory of this University, for valuable sugges- 

 tions relating to the chemical portion of this paper. 



Mineralogical Laboratory, University of Michigan, 

 Ann Arbor, Mich., November, 1905. 



* Colestin von Dorf e Dorobany bei der Stadt Hotin, Gouvernement Bessa- 

 rabien, Groth's Zeitschrif t fur Krystallographie, etc. , 1898, xxx, 319. 



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